Blinking Statistics of Small Clusters of Semiconductor Nanocrystals

Individual and small clusters of CdSe/ZnS core/shell semiconductor nanocrystals are studied with single-molecule, time-correlated, single-photon counting confocal fluorescence microscopy to obtain fluorescence intermittency (blinking) statistics and correlations. Clusters were distinguished from individual nanocrystals using intensity autocorrelations and decay histograms. Because clusters do not exhibit <i>on</i>/<i>off</i> blinking, we have constructed objective prescriptions to distinguish between <i>high</i> and <i>low</i> emission intervals using lifetime as well as intensity data. The <i>high</i>/<i>low</i> blinking of clusters is statistically similar to the <i>on</i>/<i>off</i> blinking of individual nanocrystals. These results support a model for the distinctive fluorescence properties of small nanocrystal clusters based on nonradiative energy transfer, in which the <i>high</i>/<i>low</i> blinking of a cluster is a consequence of <i>on</i>/<i>off</i> blinking of the “acceptor” (smallest energy gap) nanocrystal in the cluster